Also, fix detection of IE so it works. Apparently bowser.name !== 'IE' on IE with bowser. bowser.msie works though.

bowser correctly detects Chrome Headless as Chrome, is already used by scratchr2, and is more actively maintained than platform.

- better split of hash-parser/project-loader unit tests.

The project loader that is exported with GUI just expects to be passed projectId as a prop, and it manages loading project data.

The part of the project loader that watches for URL hash changes for the playground is a new HOC that is only used in the various playground examples.

Includes:
- context menu for switching to sliders, only on variables.
- width, height, min, max properties consumed from VM.

Update calls to addSprite2 to use new API for adding sprites. Cleanup sprite3 representation for uploading a new sprite from an image.

Also extract the "supportedBrowser" logic into a helper (rule of 3)

* Player mode

Add isPlayerOnly property on GUI. Move isFullScreen into mode reducer with isPlayerOnly.

Full screen needs to be a separate prop so that GUI knows what to show when exiting full-screen (either player-only or full editor).

- set `gui-body * {box-sizing: border-box;}` instead of expecting it to be set by the enclosing component/playground, and removed uses of content-box (adjusting sizes as needed) 
- Added `!isPlayerOnly` to the conditions for draggable sprites
- rewrote player example to use player mode.

Add more UI states (e.g. differentiating between no access, permission granted but video not loaded, video loaded). CSS cleanup.

Move runtime/renderer related code back into the vm io device. Refactor ModalVideoManager to use the video provider.

Prevent crashes resulting from the editing target not being on the target list.